A large study has found that children of women who ate little fish during pregnancy had lower IQs and more behavioral and social problems than youngsters whose mothers ate plenty of seafood, a finding that challenges the U.S. government's standard advice to limit seafood while pregnant.

The study finds "no evidence to lend support to the warning of the U.S. advisory that pregnant women should limit their seafood consumption," concluded the team led by Joseph R. Hibbeln, a researcher at the National Institute of Alcohol Abuse and Alcoholism, writing in the Lancet.

The study found that children born to women who ate about three servings of fish per week or less -- near the maximum advised by the Food and Drug Administration and the Environmental Protection Agency -- had lower verbal IQs, more problems with fine motor skills, and higher rates of behavioral and social difficulties, compared to youngsters whose mothers consumed more seafood during pregnancy.

The advice to limit seafood consumption is based on concerns that children might absorb too much methyl mercury, which builds up in fish and can cause neurological problems.

"Higher maternal fish consumption results in children showing better neurological function than children whose mothers ate low amounts of or no fish during pregnancy," Gary Myers, a professor of neurology and pediatrics at the University of Rochester Medical Center, said in an editorial accompanying the study. "These results highlight the importance of including fish in the maternal diet during pregnancy and lend support to the popular opinion that fish is brain food."

The findings are also expected to help determine whether the benefits of eating seafood for some segments of the population outweigh the risks of ingesting methyl mercury and other contaminants, including polychlorinated biphenyls (PCBs). "I think that the U.S. warnings are not meant to discourage fish consumption," said Eric Rimm, a professor of epidemiology and nutrition at the Harvard School of Public Health. He urged increased consumption of seafood during pregnancy, but excluded fish that have particularly high mercury levels: shark, swordfish, king mackerel and tilefish.

In 2001 and again in 2004, both the FDA and the EPA warned women of childbearing age, as well as those who are pregnant or nursing, and young children, to avoid consuming any of those large species.

While acknowledging that seafood can be an important part of a balanced diet, the agencies urged the public to consume a variety of fish and said that women in these groups "could safely eat 12 ounces per week of cooked fish."

In 2004, the agencies added a warning to eat no more than six ounces of albacore tuna per week.

These advisories were based on theoretical calculations, however, so Hibbeln teamed with British researchers from the University of Bristol to look more closely at the actual effects of seafood consumption in pregnant women and their children.

In 1991, the Bristol researchers had begun the Avon Longitudinal Study of Parents and Children, one of the longest and most comprehensive studies ever to assess how environmental factors, including diet, affect the development, health and well-being of children. It included more than 14,000 women and about 13,000 of their children who survived to 12 months of age.

Participants filled out food questionnaires four times during pregnancy and answered specific questions about their seafood consumption during the third trimester. Later, they provided information at regular intervals about the diet, education, social circumstances, and behavioral and developmental outcomes of their children. The children also underwent intelligence testing at age 8. Because the United Kingdom conducts national tests of students, the researchers were also able to check school test scores of children who dropped out of the study.

To the researchers' surprise, children of women consuming the most fish showed significantly higher verbal IQs at age 8 and fewer behavioral problems than youngsters whose mothers consumed only the amount of seafood recommended in the United States.

The EPA said yesterday that until the results can be reviewed and replicated, its advice would remain the same.

"EPA and FDA recommend that women of childbearing age and children eat two average meals of fish and shellfish a week of a variety of fish and shellfish that are lower in mercury, and not eat certain fish that are high in mercury," said Benjamin H. Grumbles, assistant administrator for the EPA's Office of Water.